Stick actuated inductive controller element



STICK ACTUATED INDUCTIVE CONTROLLER ELEMENT Filed April 25, 1956 G. COLLINA.

Sept. 8, 1959 5 Sheets-Sheet 1 MOE Sept. 1959 G. COLLINA 2,903,663

STICK ACTUATED INDUCTIVE CONTROLLER ELEMENT Filed April 25, 1 956 5 Sheets-Sheet 2 21 @ILZZLZ" G. C0 Lima,

STICK ACTUATED INDUCTIVE CONTROLLER ELEMENT Filed April 25, 1956 G. COLLlNA Sept. 8, 1959 5 Sheets-Sheet 3 FIG.6

Sept. 8, 1959 G. COLLlNA STICK ACTUATED INDUCTIVE CONTROLLER ELEMENT Filed April 25, 1956 5 Sheets-Sheet 4 FIG. 5

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STICK ACTUATED INDUCTIVE CONTROLLER ELEMENT Filed April 25, 1956 5 Sheets-Sheet 5 United States Patent 3 STICK ACTUATED INDUCTIVE CONTROLLER ELEMENT Giustino Coilina, Rome, Italy, assignor to Contraves Italiana, S.p.A., Rome, Italy, an Italian company Application April 25, 1956, Serial No. 580,557

Claims priority, appiication Italy May 3, 1955 10 i Claims. (Cl. 336--134) This invention relates to an inductive control device to be used as a transmitter in a follow-up system, of the type wherein the displacements of a controlling member such as a hand-lever with respect to a reference position give rise to an induced variable control current to be transmitted to a receiver operatively connected with a controlled member.

in control devices of this type, a magnetic core having an E-shaped cross-section carries on its mid-leg a primary winding fed with a reference alternating current and, on its outer legs two secondary windings connected in opposition with each other. The device is completed by an armature having the same length as the magnetic core and integral with the control lever, which is displaced in parallel relationship with said core. When the said armature is in its neutral position, i.e. when the control lever is aligned with the mid-leg of the core with the edges of the armature in front of the edges of the outer pole pieces of the said core, the primary current induces, in the secondary winding, two equal and opposed voltages, so that the resulting output voltage is nil. However, as soon as the armature is shifted outwardly in either direction, the magnetic fluxes in the outer legs of the core become different from each other, so that the induced secondary voltages are no longer mutually balanced.

In the known devices of this type, the sensitivity is practically constant. In other Words, the output voltage is substantially a linear function of the displacements of the control lever. This has many drawbacks in various applications. Thus, when progressive followup systems are actuated by means of a hand control of this type, it is often difiicult to obtain accurately adjusted small variations of the controlled member position. For example, if the device is used for controlling the rotational speed of an aided aiming system, e.g. in anti-aircraft artillery, the said device must be capable of controlling both a high rotational speed and an extremely slovv one, this last condition being indispensable when the aircraft flies substantially in radial direction with respect to the gun or when it is comparatively distant.

Moreover, these known devices are not steady at zero position. Very small alternating displacements of the hand-lever on either side of zero generate considerable currents of alternated phases, which impairs the steadiness of the whole follow-up system. Finally, these known systems are not provided with any means for stabilizing the hand-lever in the zero position nor with adjustment means for compensating mechanical defects of the assembly, so that these devices often generate, when in zero position, a considerable residual current. In some applications, such as that described above, such drawbacks are prohibitive.

The invention has for its purpose to improve inductive control devices of the type described in view of widening theirscope of application, by giving them a variable sensitivity, very small when the control member remains in the vicinity of zero position, but rapidly increasing as the control member is shifted farther. This permits disposing, on the one hand, of a large amplitude of the control current for important displacements of the control lever and, on the other hand, for the small displacements of the same, of an extremely smooth control which improves the steadiness of the whole assembly while permitting highly accurate adjustment of the controlled member.

In the known devices of the type described, the cooperating surfaces of the armature and magnetic core are cylindrical and have for their common axis that around which the armature is pivoted.

The main object of the invention is to provide the desired variable sensitivity of the control device by giving to the cylindrical surface of the armature a length greater than that of the coaxial cylindrical surface of the E- shaped core so that, in its neutral position, the armature projects on either side of the outer legs of the said core.

Computation and experience have shown that the shape of the sensitivity curve depends on the ratio s/fi between the length s of the projecting part of the armature and the gap, 5.

Another object of the invention is to further improve the shape of the said curve by giving to the edges of the armature a comparatively important thickness.

The invention has also for its purpose to provide an inductive control device as described above, further adapted to be automatically returned into zero position while offering sufficient mechanical and electrical steadiness at said zero position, which permits taking full advantage of the reduced sensitivity of the device in the vicinity of the said position.

Still another object of the invention is therefore to provide the control device with an elastic returning system continuously urging the hand-lever towards its neutral position.

In a constructive embodiment, the said returning system comprises two U-shaped members symmetrically disposed at rest on either side of a mid-reference plane containing the pivoting axis of the control lever and pivoted at the end of one of their arms around the said axis and a spring urging said members-towards each other while pressing'their'free armagainst a fixed abutment located on said line and corresponding to the zero position of the lever. The latter further carries an abutment of same diameter as the fixed abutment and clamped in neutral po sitionbetween the free arms of the U-shaped members. When the control lever isnotacted upon, the above mentioned spring holds the abutment of the control lever in the aforesaid reference plane without play or dead motion.

According to another feature of the'invention, the pivot of the control lever is secured on the frame of the apparatus on which the E-shaped core is also mounted through a system of adjusting screws adapted to vary the width of the gap either as a whole to adjust the sensitivity curve or differentially on either side of the core to adjust the symmetry and to eliminate, in Zero position, that component of the residual voltage which is in-phase with the primary voltage.

Still another object of the invention is to superpose on the output current a weak additional current drawn off of an adjustable potential divider connected across a condenser fed in series with a resistor from the secondary winding of a transformer, of which the primary winding is fed with the reference voltage.

Still a further object of the invention is to incorporate in the feeding circuit of the primary coil of the control device a phase-shifting network to balance out the phaseshift of the output current with respect to the reference voltage.

The invention also permits controlling two separate follow-up systems by means of one single control device of the type described. In this application, a control lever mounted on a swivel-joint or joy-stick is used for controlling simultaneously two diiferent effects such as corrections in azimuth and elevation in anti-aircraft artillery, or the like. According to the invention, this double control is obtained by two output currents, the sensitivity of the system being for both controls reduced in the vicinity of the zero position while it increases progressively as the control lever is shifted beyond a given limit.

For this application, it is another object of the invention to provide an inductive control device of the type described including a fixed magnetic core having the shape of a cross and having five legs, one of which, disposed at the center of the cross, carries the primary winding fed with the reference current while the four other ones, opposed pairwise carry secondary windings also connected in opposition pairwise. In this embodiment, the active surfaces of the armature and core are spherical and concentric and the armature is integral with a joystick mounted on a swivel-joint having for its center the common center of said surfaces, so that the gap has a constant value for all relative positions of the armature and core. Such inductive control devices with joy-sticks are already known, but their output currents are proportional to the angular displacements of the joy-stick as measured in two right-angled planes corresponding to the arms of the cross-shaped armature. Moreover, these known devices offer no steadiness in zero position.

In this application, in order to obtain the variable sensitivity and the mechanical and electrical steadiness according to the invention, the double control system is provided with the same improvements as the simple one, viz. projecting armature, thick edges, adjustable gap, compensating circuit for the component in quadrature of the residual voltage, phase-shifting circuit, mechanical return system, etc.

Still another object of the invention is to provide a spherical armature as described above, of which the inner face is limited along its active edges by four planes parallel to the above mentioned right-angled planes so as to avoid any interference between the two output circuits.

In a double control device of the type described, the sensitivity curves corresponding to the two right-angled planes of displacement of the lever may be diiferent. This feature may be obtained by giving to the outer core legs of one pair a greater cross-section than to those of the other pair, or by giving to the coils of one pair a greater number of turns than to those of the other pair. Alternatively, the same differential effect may be obtained by giving the armature an assymmetric shape, its projecting portion being greater in one direction than in the other. In another alternative, the pole pieces of one pair may be different in shape or size from those of the other pair.

Preferred embodiments of the invention will be hereinafter described with reference to the accompanying drawings given merely by way of example and in which:

Fig. 1 is a partly sectional view in a plane at right angles to the pivoting axis of the control lever.

Fig. 2 is a horizontal sectional view along line 2-2 of Fig. 1.

Fig. 3 is a view similar to Fig. 1, in a plane at right angles thereto. 7

Fig. 4 is an elevational view from the right of the device of Fig. 1.

Fig. 5 is a view similar to Fig. 4, but showing the control lever shifted towards the right.

Figs. 6 and 7 are diagrammatical views illustrating the operation of the control device.

Figs. 8 and 9 are curves of the output current vs. the displacements of the control lever, in Fig. 8 for a known device and in Fig. 9 for a device according to the invention, and

Fig. 10 is a wiring diagram including various correct ing networks for eliminating the residual currents.

In the preferred embodiment of the invention shown as an illustration in the drawings, a fixed magnetic circuit 11 constituted by a laminated core is provided with five legs or pole pieces each carrying a coil. The legs or pole pieces 13 are symmetric with respect to the mid-leg 12. The same is true for the legs or pole pieces 14, but in a plane at right-angles to that of the legs 13. In other Words, the four outer legs are disposed at the ends of a cross having equal arms.

The pole pieces of the legs are limited by a spherical surface the center of which coincides with the center 15 of a swivel joint having one axis in the symmetry plane of the legs 13 and its other axis in the symmetry plane of the legs 14'; both said axes are supported in bearings integral with the frame containing the apparatus and the swivel joint carries the control lever 19. The latter projects out of the frame through a gate 16 tightly closed by a flexible pleated diaphragm 17 the outer edge of which is secured on the frame while its center is attached at 18 to the control lever 19.

The lever 19 carries at its inner end a ferromagnetic armature it having a square shape when viewed in plan and its inner face that is, the one adjacent the legs of 13 and 14 is constituted by a spherical surface having its center coinciding with that of the swivel joint. The armature may be made of iron, if the apparatus is fed with an alternating current at industrial frequency but with more elevated frequency, it is preferred to make the armature of ferrite or a similar material so as to avoid magnetic losses. When the lever 19 is tilted, the armature 20 moves in front of the pole pieces of the core without any variation of the width of the gap. It is obvious that this assembly may be designed with a very high accuracy, and that means such as those described hereunder may be provided to eliminate any variation of the gap between two positions of the hand lever.

The central coil or primary winding 21 is fed with the reference alternating voltage. The two coils 22-22 carried by the pole pieces 13-13 are connected in opposition. The same is true for the coils 23-23 mounted on the pole pieces 114-14.

The coils 22-22 and 23-23 undergo induced electromagnetic forces and when the armature is in neutral (or zero) position (as shown in Figs. 1 and 3), the fluxes passing through the coils of one pair are equal to one another since the reluctances of both magnetic circuits are also equal.

The operation of the system will be best understood with reference to Figs. 6 and 7, wherein it has been assumed that the control lever 19 rotates solely around an axis at right angles to the plane of the drawing. T he length A-A' of the armature is greater than the distance 33-43 between the outer edges of the pole pieces. In Fig. 6, the projection of the armature with respect to the pole pieces, which projection is the same 011 either side when the lever is in zero position, has been indicated at s, 6 being the width of the gap, while R and S are the output terminals of the two coils. R is grounded.

In the zero position shown in Fig. 6, the reluctances in both magnetic circuits 1 and '2 are equal to one another, so that the resulting electro-magnetic force across the terminals R and S is nil. As the lever is rotated around the center 0 in the direction of the arrow, the point A first comes nearer the point B and the reluctance of the magnetic circuit 1 slightly increases and, hence, becomes slightly higher than that of the magnetic circuit 2. The gap has remained unchanged, so that only the effect of the edge of the armature acts on the reluctance. Thus, in this portion of the stroke of the lever, the sensitivity is small; in other words, the induced electro-rnag etic force is weak for a comparatively important displacement of the lever. The sensitivity is:

Where 5(a) is the output voltage and oz the angle of rotation of the control lever. As the lever is further displaced in the direction of the arrow, when the point A, after having overreached the point B, comes nearer the point C (see also Fig. 7), there is suddenly introduced a variation of the gap between the leg BC and the armature, so that the reluctance of the circuit 1 rapidly increases and, therewith, the output voltage. In these conditions, the sensitivity is extremely weak in the vicinity of the zero, while it rapidly increases for greater displacements of the lever. As mentioned in the preamble, the calculations show that the sensitivity may be influenced by adjusting the ratio of the length of the projecting edge of the armature to the width of the gap.

Figs. 8 and 9 show curves of the output current vs. the angular displacements of the control lever. Fig. 8 corresponds to a known device, wherein the length of the armaturev is equal to the distance B-B between the outer edges of the pole pieces. In such a known device, since the sensitivity is practically constant, it is too great in the vicinity of zero, where comparatively important currents are obtained in response to comparatively small displacements. As a result, it is practically impossible to obtain a fine adjustment of the controlled member. Fig. 9 corresponds to an angle of projection of the armature on either side of the core by about 3 to 4 of rotation, while the total angular stroke of the lever corresponding to the thickness of the leg is about 15. With this arrangement, the sensitivity is practically nil at zero position (tangent to the horizontal curve) and it remains weak from zero to the point B (3 to 4) to increase rapidly beyond the said point. With this arrangement, it is possible to dispose of a control current as strong as previously for important displacements, together with a great steadiness and a high accuracy in the vicinity of zero.

It is also possible to influence the curve of the output voltages by giving a certain thickness to the armature, as shown in the drawings.

It will be easily understood that the operation is similar when the armature is rotated around its other axis so that finally two separate motions may be controlled with the joy-stick. A particularly interesting application of the control device according to the invention is to be found in the field of anti-aircraft defense systems with automatic aided aiming. In this application, the operator introduces into a suitable computer initial data such as the rotational speed in azimuth and elevation, whereupon the guns, as well as the optical equipments, are rotated at said speed. In the optical apparatus, it is then possible to observe the discrepancies between the true rotational speed in azimuth and elevation and the results given by the computer. The operator then acts on a control device according to the invention for introducing corrections into the computer. It is obvious that such a system will operate if the initial data are correct for positions of the lever in the vicinity of the zero, and that, if a high accuracy is to be obtained the sensitivity on either side of the zero must be as reduced as possible. Furthermore, in the case of a course error, or if the flight speed of the aircraft suddenly varies, the operator should have facilities for introducing rapid and considerable corrections. It may be seen in Fig. 9 that thismay be easily. obtained with the device according to the invention.

Moreover, in this application, some other facilities must be also provided for automatically resetting the system to zero with a high accuracy. This is the purpose of the return device mentioned in the preamble and shown in detail in Figs. 4 and 5 for one of the rotation 5 axes. A similar device is provided for the other axis. As shown in Figs. 4 and 5, two U-shaped stirrup members 2425 are mounted to freely swing about one of the axes of the swivel joint. An abutment 26 follows the rotational motion of the control lever, while another abutment 27 is stationary. A spring 28 anchored between the two stirrup members urges the same towards each other. In the absence of any external force, the system assumes the position shown in Fig. 4 with the outturned ends of both stirrup members abutting against the stationary abutment 27 and clamping the movable abutment 26. Thus, the lever 19 is held in a well-defined stationary position which constitutes the mechanical zero of the system. When the lever is pulled towards the right, (Fig. 5), the abutment 26 pushes the stirrup member 24, while the other stirrup member 25 remains pressedagainst the stationary abutment 27 by the action of spring 28. tending to urge the lever 19 towards its at rest position with a force proportional to the amplitude of its angular shift with respect to said at rest position. The same process takes place when the lever is displaced in the opposite direction. At zero position, the spring 28. remains tightened which gives to the system a high degree of mechanical steadiness at zero position.

Fig. 3 shows similar rods 26a and 27a, a spring 28a and stirrup, 25a corresponding to the parts 26, 27, 28 and 25 and ensuring the return action in the other plane of rotation of the control lever.

As mentioned above, the horizontal cross-section of the armature preferably has a square shape since, if, for example, the cross-section of the armature were rounded, a considerable displacement of the lever around one of the axes of the swivel joint would change the projecting configuration of the edges, which would perturbate the curve output voltage/angular displacement. Conversely, when the armature has a cross-section as shown, the sensitivity curve corresponding to the angular displacement in one plane is not affected by the motions in the other plane. Now, this requires a uniform thickness of the edges of the armature. In these conditions, if the portion of the sphere constituting the armature were merely limited by four vertical planes and one horizontal plane, the edges would be thicker in the mid-portion of the sides of the armature than towards its corners, which would give rise to objectionable parasitic variations. This drawback may be easily avoided by giving to the upper face of the armature the shape of a sphere concentric to the outer face of the core.

The design of the five-leg stationary core is indicated in Figs. 1 and 3 as shown in Fig. 3, the legs 12, 1414 are constituted by fiat laminations stacked in the shape of an E' provided in its base with a mid-notch 29. As shown in Fig. l, the legs 13--13 are constituted by a stack oflaminated sheets having the general shape of a U and provided, on the upper face of the base of the U, with a notch 30. Owing to the notches 29 and 30, the U-shaped laminations may be assembled at right angles to the E-shaped ones in a five-leg core assembly.

The device further comprises means to adjust the position of the core in order to vary the gap to thereby obtain. an electrical symmetry. It also comprises means to reset the output voltage into phase with the reference voltage as well as means to balance out the component of the residual voltage in quadrature with the reference voltage. For adjustingv the symmetry of the gap, the fixed core is mounted on a platen 31 secured in turn on a ball-and-socket joint 32. Two micrometer screws 33-33 disposed under the pole pieces 13-13 are used for adjusting the gap between the said pole pieces and the armature 20. Moreover, two further micrometer screws acting under the pole pieces 14-14 are used for adjusting. the gap between the latter and the armature 20. In practice, the gap existing above one pair of pole pieces is first adjusted, whereupon the gap above the 7 other pair is adjusted in turn. Usually, a perfect adjustment will be obtained by successive approximations. Once the micrometer screws have been adjusted, they may be locked in position by means of counternuts 35 35 and 36-36.

The output voltage across the terminals of the coils is not in-phase (nor in phase opposition) with the reference voltage, due to the magnetic losses through iron. This is the reason why, according to the invention, the feeding voltage of the central coil is previously phase-shifted by a suitable angle, so as to make the output voltage continuously in phase or in phase opposition with the reference voltage. This result is obtained by means of a condenser C connected in series and a resistor R connected in parallel with the terminals of the coil 21 fed with the reference voltage V as shown in Fig. 10. Since usually the output voltage is not nil when the lever is at zero position so that a residual voltage is generated, suitable means must be provided to balance out the said residual voltage. The latter has two main components, viz. a component in phase with the reference voltage V and a component in quadrature therewith.

The first one of these components may be eliminated mechanically by suitably adjusting the gap by means of the micrometric screws described above.

As for the second one, it is eliminated, according to the invention, by feeding the secondary windings with a matching voltage of some amplitude and opposed phase. This matching voltage is obtained by means of a circuit comprising a transformer T, the primary winding of which receives the reference Voltage V, while its secondarywinding is provided with a grounded mid-tap which is connected to a resistor R and a condenser C It is then possible to draw off across the condenser C a voltage in quadrature with the reference voltage V. P- tentiometers P and P are connected across C and act as a potential divider for generating a voltage of variable amplitude phase-shifted by 90 and lagging or advancing with respect to the reference voltage. This phase-shifted voltage is sent to the coil pairs 2222 and 23-23 in order to balance out the component in quadrature.

In the embodiment described hereabove, the armature has a square cross-section while the legs of the core as well as the pole pieces l313 and 1414 are similar and While the coils 22-22 and 23-23 have the same number of turns. In this particular embodiment, it is obvious that the law of variation of the controlling eifect will be the same for both right-angled planes of displacement of the lever. As a result, for a given displacement of the lever. e.g. along the direction l313 and for the same displacement along the direction l e-14, the same output voltage will be obtained.

In an alternative embodiment, the two right-angled motions of the lever are used for controlling different follow-up systems requiring different sensitivities in the vicinity of zero as well as different output voltages. This may be easily obtained in several ways: for example, two different sensitivities in the vicinity of zero may be pro ided by giving to the projecting portion a longer length in one direction than in the other one or, in other words, by giving to the armature a rectangular crosssection instead of a square one. Alternatively, two output currents of different amplitudes may be obtained, e.g. by giving to the pole pieces of one pair, e.g. 13-13 a shape or a thickness differing from those of the other pole piece pair. It is also possible to provide, for one pair of coils, such as 2222, a greater number of turns than for the other pair.

In a general manner, while it has been, in the above description, disclosed what is deemed to be practical and efficient embodiments of the invention, it should be well understood that it is not wished to be limited thereto as there might be changes made in the arrangement,

disposition and form of the parts without departing from the principle of the present invention.

In particular, while the embodiments described are provided for controlling two servo-mechanisms with one single lever, it is clear that the invention may be used also for one single control. In that case, the armature will be limited on its lower face by a cylindrical surface coaxial with the upper surface of the three legs of the E-shaped stationary core. The functions of the projecting edges of the armature, the adjustable gap and the balancing circuits would remain the same.

Furthermore, while the advantages of the invention have been more particularly exposed in its application to the control of an anti-aircraft defense system, it is obvious that the said application is merely given as an illustration, the control device according to the invention being adapted to be used in many other types of remote control or follow-up system.

What is claimed is:

1. An inductive control device comprising, in combination, a fixed magnetic core having a central pole piece and at least one pair of outer pole pieces symmetrically disposed on either side of said central pole piece and aligned therewith, a movable control member, an armature movable with said control member in parallel relationship with said core along the direction of alignment of said pole pieces from an at rest position aligned with the axis of said central pole piece, a primary winding on said central pole piece, two secondary windings connected in series and wound in opposition, one on each of said pair of pole pieces, an alternating current source, means to feed said primary winding with current from said source, output terminals connected to said secondary windings, said armature having a length in the direction of alignment of said pole pieces greater than the distance between the outer faces of the outer pole pieces so that the armature in the at rest position projects beyond said core on opposite sides thereof, whereby as said armature is displaced to one side of said at rest position, there is fed from said secondary windings a control current increasing slowly in output voltage as long as said armature still projects beyond said core and which control current output voltage rapidly increases as the trailing edge of the armature, in the direction of its displacement, moves within the core, and further comprising means to adjust the ratio between the gap separating said armature from said pole pieces and the length of the projecting portion of the armature in at rest position.

2. An inductive control device adapted for simultaneously controlling two output control currents comprising, in combination, a fixed magnetic core having a central pole piece and four outer pole pieces symmetrically disposed pairwise on either side of said central pole piece and aligned therewith, a control member, an armature integral with said control member, a swivel-joint to pivot said control member and armature around a point located on the axis of said central pole piece, the faces of said pole pieces extending in a common spherical surface and the active face of said armature being also spherical and concentric with said common spherical surface at said point, a primary winding on said central pole piece, a first pair of secondary windings connected in series and wound in opposition, one on each of the outer pole pieces of one pair, a second pair of secondary windings connected in series and wound in opposition, one on each of the pole pieces of the other pair, an alternating current source, means to feed said primary winding with current from said source, output terminals connected to the first pair of said secondary windings, output terminals connected to the second pair of said secondary windings, said armature having dimensions transversely of the axis of the central pole piece in the respective directions aligned with the respective pairs of outer pole pieces greater than the dimensions between the outer faces of the respective pairs of outer pole pieces so that the armature overlaps all the pole pieces when the control member is in alignment with the central pole piece, and the upper face of the armature also being spherical and concentric with its inner face, so that the edges of said armature hayea uniform thickness whereby the curve of the sensitivity of control current controlled by theouter pole pieces of one pair is not influenced by the displacements of the control member in the plane of the outer pole pieces of the other pair.

3. inductive control device comprising, in combination, a fixed magnetic core having a central pole piece and at least one pair of outer pole pieces symmetrically disposed on either side of said central pole piece and aligned therewith, a movable control member, an annaturemovable with said control member in parallel relationship with said core along the direction of alignment of said pole pieces from an at rest position aligned with the axis of said central pole piece, a primary winding on said central pole piece, two secondary windings, connected in series and wound in opposition, one on each of said pair of pole pieces, an alternating current source, means to feed said primary winding with current from said source, output terminals connected to said secondary windings, saidannature having a length in the direction of alignment of said pole pieces greater than the distance'between the outer faces of the outer pole pieces so that the armature in the at rest position projects beyond said core on opposite sides thereof, whereby said armature is displaced to one side of said at rest position, there is fed from said secondary windings a control current increasing slowly in. output voltage as long as said armature still projects beyond said core and which control current output voltage rapidly increases as the trailingedge of the armature, in the direction of its displacement, moves within the core, and further comprising means to adjust the relative position of said core andjarmature.

4. An inductive control device comprising, in combination, a fixed magnetic core having a central pole piece and at least one pair of outer pole pieces symmetrically disposed on either, side. of said central pole piece and aligned therewith, a movable control member, an armature movable with said control member in parallel relationship with said core along the direction of alignment of said pole pieces from an at rest position aligned with the axis of said centralpole piece, a primary winding on said central pole piece, two secondary windings connected in series and wound in opposition, one on each of; said'pair of pole, pieces, analternating current source, means. to feed said primary winding with current from said source, output terminals, connected to said secondary windings, said, armature having a length in the direction of alignment of said pole pieces greater than the distance between the outer faces of the outer pole pieces so that the armature in the at rest position projects beyond said core on opposite sides thereof, whereby as said armature is displaced to one side of said at rest position, there is fed from said secondary windings a cont-rol current increasing slowly in output voltage as long as said armature still projects beyond said core and which control current output voltage rapidly increases as the trailing edge of the armature, in the direction of its displacement, moves within me core, and phaseshifting means interposed between said alternating current source and said primary winding to make the voltage across said secondary winding in-phase with the voltage across said alternating current source.

5. An inductive control device according to claim 4, wherein said phase-shifting means are constituted by a network including a condenser interposed between said alternating current source and said primary winding and a resistor connected with said condenser.

6. An inductive control device comprising, in combination, a fixed magnetic core having a central pole piece and at least one pair of outer pole pieces symmetrically disposed on either side of said central pole piece and aligned therewith, a movable control member, an armature movable with said control member in parallel relationship with said core along the direction of alignment of said pole pieces from an at rest position aligned with the axis of said central pole piece, two secondary windings conected in series and wound in opposition, one on each of said pair of pole pieces, an alternating current source, means to feed said primary winding with current from said source, output terminals connected to said secondary windings, said armature having a length in the direction of alignment of said pole pieces greater than the distance between the outer faces of the outer pole pieces so that the armature in the at rest position projects beyond said core on opposite sides thereof, whereby as said armature is displaced to one side of said at rest position, there is fed from said secondary windings a control current increasing slowly in output voltage as long as said armature still projects beyond said core and which control current output voltage rapidly increases as the trailing edge of the armature, in the direction of its displacement, moves within the core, and a phaseshifting network fed from said alternating current source and a potential divider fed from said phase-shifting network to feed said secondary circuit with a current of adjustable value in quadrature with the voltage across said alternating current source, to thereby balance out the component in quadrature of the residual voltage when said control member and armature are at rest.

7. An inductive control device adapted for simultaneously controlling two output control currents comprising, in combination, a fixed magnetic core having a central pole piece and four outer pole pieces symmetrically disposed pairwise on either side of said central pole piece and aligned therewith, a control member, an armature integral with said control member, a swivel-joint to pivot said control member and armature around a joint located on the axis of said central pole piece, the faces of said pole pieces extending in a common spherical surface and the active face of said armature being also spherical and concentric with said common spherical surface at said point, a primary winding on said central pole piece, a first pair of secondary windings connected in series and wound in opposition, one on each of the outer pole pieces of one pair, a second pair of secondary windings connected in series and wound in opposition, one on each of the pole pieces of the other pair, an alternating current source, means to feed said primary winding with current from said source, output terminals connected to the first pair ofsaid secondary windings, output terminals connected to the second pair of said secondary windings, said armature having dimensions transversely of the axis of the central pole piece in the respective directions aligned with the respective pairs of outer pole pieces greater than the dimensions between the outer faces of the respective pairs of outer pole pieces so that the armature overlaps all the pole pieces when the control member is in alignment with the central pole piece, said armature projecting by a greater distance in the direction of alignment of one of said outer pole piece pairs than in the direction of alignment with the other pair whereby the sensitivity curves of the second output voltages are diiferent.

8. An inductive control device adapted for simultaneously controlling two output control currents comprising, in combination, a fixed magnetic core having a central pole piece and four outer pole pieces symmetrically disposed pairwise on either side of said central pole piece and aligned therewith, a control member, an armature integral with said control member, a swivel-joint to pivot said control member and armature around a point located on the axis of said central pole piece, the faces of said pole pieces extending in a common spherical surface and the active face of said armature being also spherical and concentric with said common spherical surface at said point, a primary winding on said central pole piece, a first pair of secondary windings connected in series and wound in opposition, one on each of the outer pole pieces of one pair, a second pair of seocndary windings connected in series and wound in oposition, one on each of the pole pieces of the other pair, an alternating current source, means to feed said primary winding with current from said source, output terminals connected to the first pair of said secondary windings, output terminals connected to the second pair of said secondary windings, said armature having dimensions transversely of the axis of the central pole piece in the respective directions aligned with the respective pairs of outer pole pieces greater than the dimensions between the outer faces of the respective pairs of outer pole pieces so that the armature overlaps all the pole pieces when the control member is in alignment with the central pole piece, and the outer pole pieces of one of said pairs having a configuration different from those of the other pair, whereby the current across one of said secondary winding pairs is stronger than the current across the other secondary winding pair.

9. An inductive control device adapted for simultaneously controlling two output control currents comprising, in combination, a fixed magnetic core having a central pole piece and four outer pole pieces symmetrically disposed pairwise on either side of said central pole piece and aligned therewith, a control member, an armature integral with said control member, a swivel-joint to pivot said control member and armature around a point lo cated on the axis of said central pole piece, the faces of said pole pieces extending in a common spherical surface and the active face of said armature being also spherical and concentric with said common spherical surface at said point, a primary winding on said central pole piece, a first pair of secondary windings connected in series and wound in opposition, one on each of the outer pole pieces of one pair, a second pair of secondary windings connected in series and wound in opposition, one on each of the pole pieces of the other pair, an alternating current source, means to feed said primary winding with current' from said source, output terminals connected to the first pair of said secondary windings, output terminals connected to the second pair of said secondary windings, said armature having dimensions transversely of the axis of the central pole piece in the respective directions aligned with the respective pairs of outer pole pieces greater than the dimensions between the outer faces of the respective pairs of outer pole pieces so that the armature overlaps all the pole pieces when the control member is in alignment with the central pole piece, and the secondary windings of one of said pairs having a number of turns dilfercut from that of the secondary windings of the other pair, whereby the current across one of said pairs of secondary windings is stronger than the current across the other pair.

10. An inductive control device comprising, in combination, a fixed magnetic core having a central pole piece and at least one pair of outer pole pieces symmetrically disposed on either side of said central pole piece and aligned therewith, a movable control member, an armature movable with said control member in parallel relationship with said core along the direction of alignment of said pole pieces from an at rest position aligned with the axis of said central pole piece, a primary winding on said central pole piece, two secondary windings connectcd in series and wound in opposition, one on each of said pair of pole pieces, an alternating current source, means to feed said primary winding with current from said source, output terminals connected to said secondary windings, said armature having a length in the direction of alignment of said pole pieces greater than the distance between the outer faces of the outer pole pieces so that the armature in the at rest position projects beyond said core on opposite sides thereof, whereby as said armature is displaced to one side of said at rest position, there is fed from said secondary windings a control current increasing slowly in output voltage as long as said armature still projects beyond said core and which control cnrernt output voltage rapidly increases as the trailing edge of the armature, in the direction of its displacement, moves within the core, the faces of said pole pieces extending in a first cylindrical surface, the active face of the armature also being cylindrical and having the same axis as said first cylindrical surface, said control member being integral with said armature and pivoted around said axis, a return system including elastic means continuously urging said control member and armature into said at rest position, said return system being constituted by two stirrup members pivoted around said axis, a spring to urge said stirrup members toward each other,

a fixed abutment located between said stirrup members to define the at rest neutral position of the control member and another abutment movable with said control member and disposed between said stirrup members to transmit to the latter the returning action of said spring.

References Cited in the file of this patent UNITED STATES PATENTS 1,988,458 Minorsky Jan. 22, 1935 2,462,081 Esval Feb. 22, 1949 2,516,912 Reichel et al Aug. 1, 1950 2,592,417 Hale Apr. 8, 1952 

